The present invention relates to a heat exchanger and in particular to a plate fin heat exchanger or a primary surface heat exchanger.
Plate fin type heat exchangers generally comprise a plurality of plates, and a plurality of fins extend between and may be secured to each adjacent pair of plates. The fins may be secured to the plates by brazing, welding, diffusion bonding etc. Alternatively the fins may not be secured to the plates. The fins are defined by corrugated plates. In plate fin type heat exchangers the fins define the passages for the flow of fluids to be put into heat exchange relationship.
Primary surface type heat exchangers generally comprise a plurality of plates and a plurality of spacers extend between each adjacent pair of plates to separate the plates. In primary surface type heat exchangers the plates define passages for the flow of fluids to be put into heat exchange relationship.
Gas turbine engines comprise a compressor, a combustion chamber and a turbine arranged in flow series. The compressor compresses air and supplies it to the combustion chamber. Fuel is burnt in air in the combustion chamber to produce hot gases, which drive the turbine. The turbine drives the compressor and also drives a generator, a pump, a shaft or other load.
Heat exchangers are used in industrial gas turbine engines to return heat from the hot gases leaving the gas turbine engine to the compressed air leaving the compressor before it enters the combustion chamber. These heat exchangers are also known as recuperators, or regenerators. The recuperator heat exchanger increases the efficiency of the gas turbine engine and the hotter the air entering the combustion chamber the greater is the fuel saving.
The use of a spiral heat exchanger for a gas turbine engine recuperator is known from our European Patent EP0753712B1 and this may be a plate fin type heat exchanger or a primary surface heat exchanger.
A spiral heat exchanger, for example, is manufactured from two sheets of metal which are wound together into a spiral and the edges of the sheets of metal are joined together. The sheets of metal may be stainless steel for low temperature spiral heat exchangers or nickel base alloy for high temperature spiral heat exchangers.
One problem with the manufacture of spiral heat exchangers is ensuring close contact between the edges of the sheets of metal to enable the sheets of metal to be joined together to form a seal.
Accordingly the present invention seeks to provide a novel heat exchanger which reduces, preferably overcomes, the above mentioned problems.
Accordingly the present invention provides a heat exchanger having a hot end and a cold end, the heat exchanger comprising a first sheet and a second sheet, the first and second sheets being wound around an axis, the hot and cold ends of the heat exchanger being arranged at the axial ends of the heat exchanger, each sheet having hot and cold edge portions at the hot and cold ends respectively of the heat exchanger, at least one of the hot and cold edge portions of the first sheet being thinner and having a greater diameter than the remainder of the first sheet such that the at least one of the hot and cold edge portions of the first sheet contacts at least one of the hot and cold edge portions of the second sheet, the hot and cold edge portions of the first sheet being joined to the hot and cold edge portions of the second sheet.
Preferably both of the hot and cold edge portions of the first sheet are thinner and have a greater diameter than the remainder of the first sheet such that both of the hot and cold edge portions of the first sheet contact the hot and cold edge portions of the second sheet.
The heat exchanger may be a primary surface heat exchanger. Alternatively the heat exchanger may be a plate fin heat exchanger. At least one corrugated sheet may be arranged between the first and second sheets.
Preferably the edge portions of the sheets are joined by welded joints, brazed joints, bonded joints, crimped joints or glued joints.
Preferably the first sheet comprises a metal or alloy. Preferably the second sheet comprises a metal or alloy. Preferably the alloy comprises a nickel base alloy or steel. Preferably the alloy comprises stainless steel.
Preferably the heat exchanger is a spiral heat exchanger.
The present invention also provides a method of manufacturing a heat exchanger, the heat exchanger having a hot end and a cold end, the hot and cold ends of the heat exchanger being arranged at the axial ends of the heat exchanger, comprising forming a first sheet, the first sheet having hot and cold edge portions, thinning at least one of the hot and cold edge portions of the first sheet such that the at least one of the hot and cold edge portions is thinner and longer than the remainder of the first sheet, forming a second sheet, the second sheet having hot and cold edge portions, winding the first and second sheets together around an axis such that the first sheet is within the second sheet and such that the at least one of the hot and cold edge portions of the first sheet has a greater diameter than the remainder of the first sheet such that the at least one of the hot and cold edge portions of the first sheet contacts the at least one of the hot and cold edge portions of the second sheet, and joining the hot and cold edge portions of the first sheet to the hot and cold edge portions of the second sheet.
Preferably the method comprises thinning both of the hot and cold edge portions of the first sheet such that both of the hot and cold edge portions are thinner and have a greater diameter than the remainder of the first sheet such that both of the hot and cold edge portions of the first sheet contact the hot and cold edge portions of the second sheet.
The heat exchanger may be a primary surface heat exchanger. Alternatively the heat exchanger may be a plate fin heat exchanger. The method may comprise placing at least one corrugated sheet between the first and second sheets and winding the first and second sheets and the at least one corrugated sheet into a spiral.
Preferably the joining of the edge portions of the first and second sheets comprises welding, brazing, bonding, crimping or gluing.
Preferably the method comprises forming the first sheet from a metal or alloy. Preferably the method comprises forming the second sheet from a metal or alloy. Preferably the alloy comprises a nickel base alloy or steel. Preferably the alloy comprises stainless steel.
Preferably the thinning of the at least one hot and cold edge portion of the first sheet comprises rolling or hammering.
Preferably the first and second sheets are wound into a spiral to form a spiral heat exchanger.